In some connections between devices, such as a USB connection, one device may assume the role of a host device and another device may assume the role of an accessory device. A vehicle system may have an on-board computer system (such as an infotainment system) that can act as the host device and a mobile device (such as a smartphone) that is connected to it may assume the role of an accessory. It may be difficult or impossible to access instructions and other communications between the vehicle system and the mobile device for the purpose, for example, of troubleshooting, diagnostics and the like.